ELECTROCHEMICAL CELL

Last Update 06/ 06/ 2008

in English/ in Esperanto/ in Portuguese

The electrochemical cell represented below in the interactive scheme has two compartments filled with their respective reagents in aqueous solution at activity = 1.0. The temperature is 25.0 oC. One of the electrodes is the standard hydrogen electrode in order to measure the standard equilibrium potential of the cell. For introductory chemistry the concentrations of the aqueous species may be sufficiently good if equal to 1.0 M. The required hydrogen fugacity is 1.0. This may be acceptably replaced by an equal value in atmosphere units. The two compartments are connected by a salt bridge and two electrodes connected to an external circuit to a digital voltmeter. Any good general chemistry book will inform on the several details of this experiment. The components that take part in the chemical reaction defining the cell are indicated in the respective cell compartment. The salt bridge is here a potassium chloride solution kept inside an inverted U tube. The voltmeter probe lead labeled C (common, also named earth), is directed to compartment at the left side and the red colored led directed to the other electrode. When the electrons try to flow from the electrode at left to that at the right side and consequently from C to the red connection, the voltage will have a positive sign. This indicates the electric current i of the external circuit is running the reverse path. The very high resistance of the voltmeter does not allow the electron flow. When the voltmeter is substituted by another device with lower resistance or by a suitable lamp, the effective electron flow will happen from the electrode where the chemical reaction of oxidation occurs, named anode to the compartment of reduction, named cathode. On the other hand, when a conducting wire connects both electrodes the cell is said to be in short-circuit. In this case the electron speed on the wire will be maximum.
A click on button A in the lower part of the interactive scheme will substitute the experiment by another.

Exercise

You are invited to write the spontaneous chemical equation that would occur for the actual cell connected in short-circuit.

Please send your comments.

Table of subjects.
Presentation
Chemistry Analytical Chromatography
Elemental organic analysis
Volumetric analysis, simulation
Crystallography 3 fold screw axis
4 fold inversion axis on tetrahedron
5 fold rotation axis absent in crystallography
Binary axis and reflection plane in stereographic projection
Bravais lattices
Conic sections under symmetry operators
Converting from spherical coordinates to stereographic projection
Crystal lattice and unit cell
Determination of unit cell
Elements of symmetry in action - animation
Elements of symmetry in action - cube game
Elements of symmetry in action - dodecahedron game
Elements of symmetry in action - icosahedron game
Elements of symmetry in action - octahedron game
Elements of symmetry in action - tetrahedron game
Ewald sphere and crystal measurements
Extinctions
Five classes in the cubic system
Five classes in the rhombohedral system
From tetrahedron to prism
Gnomonic projection
Improper symmetry axis
Miller indices
Miller indices - animation
Miller indices - cube game
Miller indices - octahedron game
Miller indices - rhombic dodecahedron game
Miller indices - tetrahedron game
Mirror plane
Orientations of the cube
Plane symmetry groups
Question on point group
Rotation axis in octahedron and Werner compounds
Rotation axis on tetrahedron and organic molecules
Rotation of the parallel and stereographic projections of the cube
Seven faces in stereographic projection
Seven classes in the hexagonal system
Seven classes in the tetragonal system
Six elements of symmetry in seven orientations
Spherical projection of the octahedron
Stereographic projection
Stereographic projection of six polyhedra in different orientations
Straight line equations and symmetry elements
Symmetry, 2 fold axis
Symmetry, 2, 3 and 6 fold axis in benzene
Symmetry, 3 fold axis in the cube
Symmetry, 4 fold axis in the cube
Symmetry, 4 fold axis in the unit cell of gold
Symmetry elements and Miller indices game
Symmetry elements and Miller indices game - octahedron
Symmetry in art and in crystallography
Three classes in the monoclinic system
Three classes in the orthorhombic system
Twin crystals
Two classes in the triclinic system
Unit cell in hexagonal net
General Butane conformations
Density
Electrochemical cell
Ethane conformations
Resources of chemical-ICT: water, health and symmetry
Solid and liquid gold